Note its relatively large size, and the constrictions that give a false impression of segmentation. My techs call this a bubblegum appearance, which I think you can appreciate in this case:
Macrocanthorhynchus species have a retractable proboscis, which proved to be quite difficult to see in this case. Florida Fan nicely solved this problem by having histologic sections made of the anterior end:
Although I didn't provide enough features for species identification, Florida Fan noted that the morphology is consistent with M. ingens: "The proboscis measures ~500 µm in width and ~650 µm long, much smaller than that of M. hirudinaceus." The geographic distribution (Southeastern United States) also fits with this species. Blaine Mathison, Henry Bishop, Richard Bradbury and others published a very similar case 2 years ago that you can read HERE. It contains a lot of interesting information about the lifecycle, morphologic features and treatment of M. ingens (for example, human infection may be acquired by eating millipedes). Acanthocephalans are more closely related to rotifers than nematodes; hence Blaine's mention of rotifers in the comments.
Florida Fan seems to get a lot of these cases! HERE is one that he donated back in 2013 which nicely shows the eggs of Macracanthorhynchus. You can't tell M. hirudinaceus from M. ingens by its eggs, unfortunately. Take a look at the previous case for more information and a nice poem by Blaine.
This week's case is a nice straight-forward one - I promise, no tricks! Please identify the following worm. She was ripped in half and only the anterior end was submitted to us. If intact, she would have measured approximately 1 cm long.
Answer: Enterobius vermicularis
As noted by Florida Fan, the diagnostic features shown in this case include the cephalic alae, esophageal bulb, and "D-shaped" eggs (oval with a flattened side). Natalie Ellis described them as 'coffee bean' or 'paper weight' shaped - I had never heard those analogies before!
Thanks to Bernardino Rocha and Silvia for the interesting comments about the different Oxyuroidea found in mammals, reptiles and amphibians (see the comments section on this post for the full details). Thank you also to Old One who reminded us that dogs and cats do not have pinworm and are not the source of your child's infection! I'm amazed that this connection would be made, given how ubiquitous pinworms are. Infection could almost be considered a right of passage in childhood.
Infection is usually diagnosed based on the clinical symptoms (nocturnal pruritus ani) and identification of eggs +/- adult females on the cellulose tape test. Just yesterday I had the privilege of visiting the Meguro Parasitological Museum in Tokyo and got to see their large array of fascinating specimens. Here are a couple of images from their museum:
Japanese 'tape prep' kit:
Statistics showing a significant decline in pinworm infections in Japan - likely due to the required annual tape prep exams that are obtained for all school-aged children (see an interesting blog post from a mom on this topic HERE):
And finally, a lovely poem by Blaine: Dwelling deep down in the lumen of your large intestine a female pinworm is making her way to the perianal skin for before the rooster crows she'll lay eggs in droves that are going to cause your booty to start itchin'
Every week I will post a new Case, along with the answer to the previous case. Please feel free to write in with your answers, comments, and questions. Also check out my image archive website at http://parasitewonders.com. Enjoy!
The Fine Print: Please note that all opinions expressed here are mine and not my employer. Information provided here is for educational purposes only. It is not intended as and does not substitute for medical advice. I do not accept medical consults from patients.